Seats in vehicles such as aircraft include frames for supporting cushions, pads, and other seating components. A frame can include one or more base-frame tubes capable of providing support when the seat experiences stresses caused by an individual in the seat during a crash landing condition or caused by other activities. A base-frame tube includes a main tube and a second tube located in the inner diameter of the main tube. The second tube can provide local reinforcement to the main tube. The main tube and the second tube are fastened together using rivets. The base-frame tube has a constant outer diameter.
Each of the main tube and the second tube has sidewalls of consistent thickness. The tubes are often made from extruded or drawn metal, such as aluminum or steel. When loads are placed on the tubes, the second tube can change position in the inner diameter of the main tube and cause uneven distribution of forces from stress at the abrupt transitions in overall tube sidewall thickness. Furthermore, such tube configurations can be relatively heavy.
Accordingly, tubes are desirable that can distribute loads more evenly. Tubes are also desirable that weigh less and that can require less assembly time. Tubes are also desirable that are configured to prevent the tubes from decoupling from additional components of frames.